Catalase takes part in rat liver mitochondria oxidative stress defense

Estimation of the hydrogen peroxide producing capacities of liver and cardiac mitochondria isolated from C57BL/6N and C57BL/6J mice

Here, we examined the hydrogen peroxide (H₂O₂) producing capacities of pyruvate dehydrogenase (PDH), α-ketoglutarate dehydrogenase (KGDH), proline dehydrogenase (PRODH), glycerol-3-phosphate dehydrogenase (G3PDH), succinate dehydrogenase (SDH; complex II), and branched-chain keto acid dehydrogenase (BCKDH), in cardiac and liver mitochondria isolated from C57BL/6N (6N) and C57BL/6J (6J) mice. Various inhibitor combinations were used to suppress ROS production by complexes I, II, and III and estimate the native rates of H₂O₂ production for these enzymes. Overall, liver mitochondria from 6N mice produced ∼2-fold more ROS than samples enriched from 6J mice. This was attributed, in part, to the higher levels of glutathione peroxidase-1 (GPX1) and catalase (CAT) in 6J mitochondria. Intriguingly, PDH, KGDH, and SDH comprised up to ∼95% of the ROS generating capacity of permeabilized 6N liver mitochondria, with PRODH, G3PDH, and BCKDH making minor contributions. By contrast, BCKDH accounted for ∼34% of the production in permeabilized 6J mitochondria with KGDH and PRODH accounting for ∼23% and ∼19%. G3PDH produced high amounts of ROS, accounting for ∼52% and ∼39% of the total H₂O₂ generating capacity in 6N and 6J heart mitochondria. PRODH was also an important ROS source in 6J mitochondria, accounting for ∼43% of the total H₂O₂ formed. In addition, 6J cardiac mitochondria produced significantly more ROS than 6N mitochondria. Taken together, our findings demonstrate that these other generators can also serve as important sources of H₂O₂. Additionally, we found that mouse strain influences the rate of production from the individual sites that were studied.

Circadian Regulation of Mitochondrial Dynamics in Retinal Photoreceptors

Energy expenditure and metabolism in the vertebrate retina are under circadian control, as we previously reported that the overall retinal ATP content and various signaling molecules related to metabolism display daily or circadian rhythms. Changes in the fission and fusion process of mitochondria, the major organelles producing ATP, in retinal photoreceptors are largely dependent on light exposure, but whether mitochondrial dynamics in photoreceptors and retinal neurons are under circadian control is not clear. Herein, we investigated the possible roles of circadian oscillators in regulating mitochondrial dynamics, mitophagy, and redox states in the chicken retina and mammalian photoreceptors. After entrainment to 12:12-h light-dark (LD) cycles for several days followed by free-running in constant darkness (DD), chicken embryonic retinas and cone-derived 661W cells were collected in either LD or DD at 6 different zeitgeber time (ZT) or circadian time (CT) points. The protein expression of mitochondrial dynamin-related protein 1 (DRP1), mitofusin 2 (MFN2), and PTEN-induced putative kinase 1 (PINK1) displayed daily rhythms, but only DRP1 was under circadian control in the chicken retinas and cultured 661W cells. In addition, cultured chicken retinal cells responded to acute oxidative stress differently from 661W cells. Using pMitoTimer as a mitochondrial redox indicator, we found that the mitochondrial redox states were more affected by light exposure than regulated by circadian oscillators. Thus, this study demonstrates that the influence of cyclic lights might outweigh the circadian regulation of complex mitochondrial dynamics in light-sensing retinal cells.

Safety assessment of cefuroxime on male reproductive system: Subacute toxicity and potential reversibility after a complete cycle of spermatogenesis and epididymal maturation in Wistar rats

The effects of cefuroxime on reproductive system were investigated in male rats. Doses of 0, 30, 60 or 120 mg/kg of cefuroxime were intraperitoneally injected daily, for 7 days. Half of the rats were euthanized 24 h after the last dose and other half were induced to death 70 days after the last treatment. After 8 days of the experiment, results showed that cefuroxime induced a significant reduction in the weights of testes, epididymis and accessory sex organs. In addition, it decreased sperm quality, plasma testosterone level, and antioxidant enzyme activities while increasing the level of malondialdehyde. After a complete cycle of spermatogenesis and epididymal maturation, the results indicated complete reversibility of the adverse effects previously mentioned. In conclusion, cefuroxime induced reversible dose-dependent adverse effects on testicular and epididymal functions of rats.

Glutathione content and expression of proteins involved with glutathione metabolism differs in longissimus dorsi, subcutaneous adipose, and liver tissues of finished vs. growing beef steers

Increased tissue redox state may result in sub-optimal growth. Our goal was to determine if glutathione (GSH) content and expression of proteins involved with GSH metabolism change in longissimus dorsi (LD), subcutaneous adipose (SA), and liver tissues of growing vs. finishing steer phenotypes. Tissues were taken from 16 Angus steers (BW = 209 ± 29.4 kg) randomly assigned (n = 8) to develop through Growing (final BW = 301 ± 7.06 kg) vs. Finished (final BW = 576 ± 36.9 kg) growth phases, and at slaughter had achieved different rib-eye area (REA) (53.2, 76.8 cm2), marbling scores (296, 668), and 12th rib adipose thickness (0.54, 1.73 cm), respectively (Amino Acids, doi:10.1007/s00726-018-2540-8). GSH content (mg/g wet tissue) was determined by a commercial assay and the relative content of target protein and mRNA in tissue homogenates was determined by Western blot and reverse-transcribed PCR analyses, respectively. The effect of growth phase (Finished vs. Growing) was assessed by ANOVA using the GLM procedure of SAS. The LD of Finished steers had more (P < 0.04) GSH (42%) and GSH synthesizing (GCLC, 61%; GCLM, 21%) and metabolizing (GPX1, 42%; GPX3, 73%; GGT1, 56%) enzymes, and less (P < 0.02) GPX2 (46%), EAAC1 (30%) and glutamine synthetase (GS) (28%), whereas GTRAP3-18 and ARL6IP1 did not differ (P > 0.57). Principal component analysis found that GSH content of LD was associated with REA and marbling score. The SA of Finished steers had less (P < 0.04) GSH (38%), GSH metabolizing (GPX4, 52%; GGT1, 71%) enzyme mRNA, and GTRAP3-18 (123%) and ARL6IP1 (43%), whereas the mRNA content of GSH-synthesizing enzymes and content of EAAC1 and GS did not differ (P > 0.32). The liver of Finished steers had less (P < 0.02) mRNA content of GSH synthesizing (GCLC, 39%; GSS 29%) and metabolizing (GPX1, 30%) enzymes, and more (P < 0.01) GSTM1 metabolizing enzyme (114%). The change in GSH content as steers fattened indicate an increased antioxidant capacity in the LD of Finished steers, and a decreased antioxidant capacity in SA, consistent with changes in enzyme and transporter expression. Changes in liver enzyme and transporter expression were consistent with no change in GSH content. The relationship of EAAC1 regulatory proteins (GTRAP3-18, ARL6IP1) to GSH, EAAC1, and GS content differs and changes as Growing steers develop into Finished phenotypes. These findings provide mechanistic insight into how antioxidant capacity occurs in tissues of economic and metabolic importance as cattle fatten.

Allium porrum and Bauhinia Variegata Mitigate Acute Liver Failure and Nephrotoxicity Induced by Thioacetamide in Male Rats

The present work has been designed to investigate the hepatoprotective and renoprotective efficiency of alcoholic extract of Allium porrum and Bauhinia variegata leaves in thioacetamide-induced toxicity in adult Wistar rats. Allium porrum leaf extract, Bauhinia variegata leaf extract and their combinations were orally administered for 14 days then TAA (300 mg/kg) i.p. was injected once and the rats were sacrificed 2 days later. Plasma AST, ALT, GGT, total bilirubin, creatinine, urea, uric acid, triglyceride, cholesterol, HDL and LDL were measured. Liver MDA, GSH, CAT, SOD and TNF-α were evaluated. Histological examination was performed. The rats treated with TAA showed a significant increase in AST, ALT, GGT, total bilirubin, creatinine, urea, uric acid, total, triglyceride, cholesterol and HDL while it led to a significant decrease in protein and HDL. The treatment of rats with TAA resulted in a significant decrease of the hepatic GSH, SOD and CAT and a significant elevation of MDA and TNF-α. Allium porrum and Bauhinia variegata extracts alleviated the toxic effects of TAA on the liver and the kidney. In conclusion, treatment with Allium porrum and Bauhinia variegata extracts and their combination reduced deleterious effects of TAA on liver through antioxidant and anti-inflammatory properties.

Rapid peroxynitrite reduction by human peroxiredoxin 3: Implications for the fate of oxidants in mitochondria

Mitochondria are main sites of peroxynitrite formation. While at low concentrations mitochondrial peroxynitrite has been associated with redox signaling actions, increased levels can disrupt mitochondrial homeostasis and lead to pathology. Peroxiredoxin 3 is exclusively located in mitochondria, where it has been previously shown to play a major role in hydrogen peroxide reduction. In turn, reduction of peroxynitrite by peroxiredoxin 3 has been inferred from its protective actions against tyrosine nitration and neurotoxicity in animal models, but was not experimentally addressed so far. Herein, we demonstrate the human peroxiredoxin 3 reduces peroxynitrite with a rate constant of 1 × 10⁷ M^-1 s^-1 at pH 7.8 and 25 °C. Reaction with hydroperoxides caused biphasic changes in the intrinsic fluorescence of peroxiredoxin 3: the first phase corresponded to the peroxidatic cysteine oxidation to sulfenic acid. Peroxynitrite in excess led to peroxiredoxin 3 hyperoxidation and tyrosine nitration, oxidative post-translational modifications that had been previously identified in vivo. A significant fraction of the oxidant is expected to react with CO₂ and generate secondary radicals, which participate in further oxidation and nitration reactions, particularly under metabolic conditions of active oxidative decarboxylations or increased hydroperoxide formation. Our results indicate that both peroxiredoxin 3 and 5 should be regarded as main targets for peroxynitrite in mitochondria.

Mitochondrial calcium transport and the redox nature of the calcium-induced membrane permeability transition

Mitochondria possess a Ca²⁺ transport system composed of separate Ca²⁺ influx and efflux pathways. Intramitochondrial Ca²⁺ concentrations regulate oxidative phosphorylation, required for cell function and survival, and mitochondrial redox balance, that participates in a myriad of signaling and damaging pathways. The interaction between Ca²⁺ accumulation and redox imbalance regulates opening and closing of a highly regulated inner membrane pore, the membrane permeability transition pore (PTP). In this review, we discuss the regulation of the PTP by mitochondrial oxidants, reactive nitrogen species, and the interactions between these species and other PTP inducers. In addition, we discuss the involvement of mitochondrial redox imbalance and PTP in metabolic conditions such as atherogenesis, diabetes, obesity and in mtDNA stability.

Neuroprotective role of hyperforin on aluminum maltolate-induced oxidative damage and apoptosis in PC12 cells and SH-SY5Y cells

Many reports demonstrated that aluminum maltolate (Almal) has potential toxicity to human and animal. Our study has demonstrated that Almal can induce oxidative damage and apoptosis in PC12 cells and SH-SY5Y Cells, two in vitro models of neuronal cells. Hyperforin (HF) is a well-known antioxidant, anti-inflammatory, anti-amyloid and anti-depressant compound extracted from Hypericum perforatum extract. Here, we investigated the neuroprotective effect of HF against Almal-induced neurotoxicity in cultured PC12 cells and SH-SY5Y cells, mainly caused by oxidative stress. In the present study, HF significantly inhibited the formation of reactive oxygen species (ROS), decreased the level of lipid peroxide and enhanced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) compared with Almal group in PC12 cells and SH-SY5Y cells. Additionally, HF suppressed the reduction of the mitochondrial membrane potential (MMP), cytochrome c (Cyt-c) release, activation of caspase-3, and the down-regulation of Bcl-2 expression and up-regulation of Bax expression induced by Almal in PC12 cells and SH-SY5Y cells. In summary, HF protects PC12 cells and SH-SY5Y cells from damage induced by Almal through reducing oxidative stress and preventing of mitochondrial-mediated apoptosis.

Mitochondrial Uptake and Accumulation of Vitamin C: What Can We Learn from Cell Culture Studies?

SIGNIFICANCE

The mitochondrial fraction of l-ascorbic acid (AA) is of critical importance for the regulation of the redox status of these organelles and for cell survival. Recent Advances: Most cell types take up AA by the high-affinity sodium-dependent vitamin C transporter 2 (SVCT2) sensitive to inhibition by dehydroascorbic acid (DHA). DHA can also be taken up by glucose transporters (GLUTs) and then reduced back to AA. DHA concentrations, normally very low in biological fluids, may only become significant next to superoxide-releasing cells. Very little is known about the mechanisms mediating the mitochondrial transport of the vitamin.

CRITICAL ISSUES

Information on AA transport is largely derived from studies using cultured cells and is therefore conditioned by possible cell culture effects as overexpression of SVCT2 in the plasma membrane and mitochondria. Mitochondrial SVCT2 is susceptible to inhibition by DHA and transports AA with a low affinity as a consequence of the restrictive ionic conditions. In some cells, however, high-affinity mitochondrial transport of AA is observed. Mitochondrial uptake of DHA may take place through GLUTs, an event followed by its prompt reduction to AA in the matrix. Intracellular levels of DHA are, however, normally very low.

FUTURE DIRECTIONS

We need to establish, or rule out, the role and significance of mitochondrial SVCT2 in vivo. The key question for mitochondrial DHA transport is instead related to its very low intracellular concentrations.

H2O2 metabolism in liver and heart mitochondria: Low emitting-high scavenging and high emitting-low scavenging systems

Although mitochondria are presumed to emit and consume reactive oxygen species (ROS), the quantitative interplay between the two processes in ROS regulation is not well understood. Here, we probed the role of mitochondrial bioenergetics in H₂O₂ metabolism using rainbow trout liver and heart mitochondria. Both liver and heart mitochondria emitted H₂O₂ at rates that depended on their metabolic state, with the emission rates (free radical leak) constituting 0.8-2.9% and 0.2-2.5% of the respiration rate in liver and heart mitochondria, respectively. When presented with exogenous H₂O₂, liver and heart mitochondria consumed it by first order reactions with half-lives (s) of 117 and 210, and rate constants of 5.96 and 3.37 (× 10^-3 s^-1), respectively. The mitochondrial bioenergetic status greatly affected the rate of H₂O₂ consumption in heart but not liver mitochondria. Moreover, the activities and contribution of H₂O₂ scavenging systems varied between liver and heart mitochondria. The significance of the scavenging systems ranked by the magnitude (%) of inhibition of H₂O₂ removal after correcting for emission were, liver (un-energized and energized): catalase > glutathione (GSH) ≥ thioredoxin reductase (TrxR); un-energized heart mitochondria: catalase > TrxR > GSH and energized heart mitochondria: GSH > TrxR > catalase. Notably, depletion of GSH evoked a massive surge in H₂O₂ emission that grossly masked the contribution of this pathway to H₂O₂ scavenging in heart mitochondria. Irrespective of the organ of their origin, mitochondria behaved as H₂O₂ regulators that emitted or consumed it depending on the ambient H₂O₂ concentration, mitochondrial bioenergetic state and activity of the scavenging enzyme systems. Indeed, manipulation of mitochondrial bioenergetics and H₂O₂ scavenging systems caused mitochondria to switch from being net consumers to net emitters of H₂O₂. Overall, our data suggest that the low levels of H₂O₂ typically present in cells would favor emission of this metabolite but the scavenging systems would prevent its accumulation.

Catalase and nonalcoholic fatty liver disease

Obesity and insulin resistance are considered the main causes of nonalcoholic fatty liver disease (NAFLD), and oxidative stress accelerates the progression of NAFLD. Free fatty acids, which are elevated in the liver by obesity or insulin resistance, lead to incomplete oxidation in the mitochondria, peroxisomes, and microsomes, leading to the production of reactive oxygen species (ROS). Among the ROS generated, H₂O₂ is mainly produced in peroxisomes and decomposed by catalase. However, when the H₂O₂ concentration increases because of decreased expression or activity of catalase, it migrates to cytosol and other organelles, causing cell injury and participating in the Fenton reaction, resulting in serious oxidative stress. To date, numerous studies have been shown to inhibit the pathogenesis of NAFLD, but treatment for this disease mainly depends on weight loss and exercise. Various molecules such as vitamin E, metformin, liraglutide, and resveratrol have been proposed as therapeutic agents, but further verification of the dose setting, clinical application, and side effects is needed. Reducing oxidative stress may be a fundamental method for improving not only the progression of NAFLD but also obesity and insulin resistance. However, the relationship between NAFLD progression and antioxidants, particularly catalase, which is most commonly expressed in the liver, remains unclear. Therefore, this review summarizes the role of catalase, focusing on its potential therapeutic effects in NAFLD progression.

Oxidative responses and fungal infection biology

The balance between reactive oxygen species and reactive nitrogen species production by the host and stress response by fungi is a key axis of the host-pathogen interaction. This review will describe emerging themes in fungal pathogenesis underpinning this axis.

Carcass traits, meat quality, antioxidant status and antioxidant gene expression in muscle and liver of Hu lambs fed perilla seed

The effects of perilla (Perilla frutescens L.) seed on carcass traits, meat quality, antioxidant status and antioxidant gene expression in the liver and muscle of Hu lambs were investigated in this study. Sixty Hu lambs (23.02 ± 1.36 kg) were randomly divided into four experimental groups receiving diets containing 0%, 5%, 10% or 15% perilla seed (CD, 5%PFSD, 10%PFSD and 15%PFSD, respectively). The addition of perilla seed had no significant impacts on carcass traits (p > .05). There were no differences in pH, meat colour, drip loss, cooking loss or shear force among the four treatments (p > .05). Addition of perilla seed increased (p < .05) deposition of intramuscular lipids but had no effect on other chemical components in the longissimus dorsi (LD) (p > .05). The 15%PFSD diet decreased the total antioxidant capacity (T-AOC) and malondialdehyde (MDA) content in the liver (p < .05 for both) but increased the activity of these antioxidant enzymes in LD (p < .05 for both). Compared to CD, addition of perilla seed increased superoxide dismutase (SOD) and glutathione peroxidase (GPX) expression in the liver and LD (p < .05 for all). These results indicate that perilla seed supplementation in lambs' diets can increase deposition of intramuscular lipids and improve muscular oxidative status and meat quality.

Hydroethanolic Extract of Strychnos pseudoquina Accelerates Skin Wound Healing by Modulating the Oxidative Status and Microstructural Reorganization of Scar Tissue in Experimental Type I Diabetes

The effect of topical application of ointment based on Strychnos pseudoquina hydroethanolic extract in the cutaneous wounds healing in diabetic rats was evaluated. Samples of S. pseudoquina were submitted to phytochemical prospection and in vitro antioxidant assay. Thirty Wistar rats were divided into 5 groups: Sal-wounds treated with 0.9% saline solution; VH-wounds treated with 0.6 g of lanolin cream (vehicle); SS-wounds treated with silver sulfadiazine cream (10 mg/g); ES5- and ES10-wounds treated with an ointment of S. pseudoquina extract, 5% and 10%, respectively. Fragments of wounds were removed for histological and biochemical analysis every 7 days during 21 days. ES showed equivalent levels per gram of extract of total phenols and flavonoids equal to 122.04 mg for TAE and 0.60 mg for RE. The chlorogenic acid was one of the major constituents. S. pseudoquina extract presented high antioxidant potential in vitro. ES5 and ES10 showed higher wound healing rate and higher amount of cells, blood vessels, and type III and I collagen. The oxidative stress markers were lower in the ES5 and ES10 groups, while the antioxidants enzymes levels were higher. Ointment based on S. pseudoquina extract promotes a fast and efficient cutaneous repair in diabetic rats.

Examination of the superoxide/hydrogen peroxide forming and quenching potential of mouse liver mitochondria

Pyruvate dehydrogenase (PDHC) and α-ketoglutarate dehydrogenase complex (KGDHC) are important sources of reactive oxygen species (ROS). In addition, it has been found that mitochondria can also serve as sinks for cellular hydrogen peroxide (H₂O₂). However, the ROS forming and quenching capacity of liver mitochondria has never been thoroughly examined. Here, we show that mouse liver mitochondria use catalase, glutathione (GSH), and peroxiredoxin (PRX) systems to quench ROS. Incubation of mitochondria with catalase inhibitor 3-amino-1,2,4-triazole (triazole) induced a significant increase in pyruvate or α-ketoglutarate driven O₂^-/H₂O₂ formation. 1-Choro-2,4-dinitrobenzene (CDNB), which depletes glutathione (GSH), elicited a similar effect. Auranofin (AF), a thioredoxin reductase-2 (TR2) inhibitor which disables the PRX system, did not significantly change O₂^-/H₂O₂ formation. By contrast catalase, GSH, and PRX were all required to scavenging extramitochondrial H₂O₂. In this study, the ROS forming potential of PDHC, KGDHC, Complex I, and Complex III was also profiled. Titration of mitochondria with 3-methyl-2-oxovaleric acid (KMV), a specific inhibitor for O₂^-/H₂O₂ production by KGDHC, induced a ~86% and ~84% decrease in ROS production during α-ketoglutarate and pyruvate oxidation. Titration of myxothiazol, a Complex III inhibitor, decreased O₂^-/H₂O₂ formation by ~45%. Rotenone also lowered ROS production in mitochondria metabolizing pyruvate or α-ketoglutarate indicating that Complex I does not contribute to ROS production during forward electron transfer from NADH. Taken together, our results indicate that KGDHC and Complex III are high capacity sites for O₂^-/H₂O₂ production in mouse liver mitochondria. We also confirm that catalase plays a role in quenching either exogenous or intramitochondrial H₂O₂.

Fructose-Rich Diet Affects Mitochondrial DNA Damage and Repair in Rats

Evidence indicates that many forms of fructose-induced metabolic disturbance are associated with oxidative stress and mitochondrial dysfunction. Mitochondria are prominent targets of oxidative damage; however, it is not clear whether mitochondrial DNA (mtDNA) damage and/or its lack of repair are events involved in metabolic disease resulting from a fructose-rich diet. In the present study, we evaluated the degree of oxidative damage to liver mtDNA and its repair, in addition to the state of oxidative stress and antioxidant defense in the liver of rats fed a high-fructose diet. We used male rats feeding on a high-fructose or control diet for eight weeks. Our results showed an increase in mtDNA damage in the liver of rats fed a high-fructose diet and this damage, as evaluated by the expression of DNA polymerase γ, was not repaired; in addition, the mtDNA copy number was found to be significantly reduced. A reduction in the mtDNA copy number is indicative of impaired mitochondrial biogenesis, as is the finding of a reduction in the expression of genes involved in mitochondrial biogenesis. In conclusion, a fructose-rich diet leads to mitochondrial and mtDNA damage, which consequently may have a role in liver dysfunction and metabolic diseases.

Simplified qPCR method for detecting excessive mtDNA damage induced by exogenous factors

Damage to mitochondrial DNA (mtDNA) is a meaningful biomarker for evaluating genotoxicity of drugs and environmental toxins. Existing PCR methods utilize long mtDNA fragments (∼8-10kb), which complicates detecting exact sites of mtDNA damage. To identify the mtDNA regions most susceptible to damage, we have developed and validated a set of primers to amplify ∼2kb long fragments, while covering over 95% of mouse mtDNA. We have modified the detection method by greatly increasing the enrichment of mtDNA, which allows us solving the problem of non-specific primer annealing to nuclear DNA. To validate our approach, we have determined the most damage-susceptible mtDNA regions in mice treated in vivo and in vitro with rotenone and H₂O₂. The GTGR-sequence-enriched mtDNA segments located in the D-loop region were found to be especially susceptible to damage. Further, we demonstrate that H₂O₂-induced mtDNA damage facilitates the relaxation of mtDNA supercoiled conformation, making the sequences with minimal damage more accessible to DNA polymerase, which, in turn, results in a decrease in threshold cycle value. Overall, our modified PCR method is simpler and more selective to the specific sites of damage in mtDNA.

Effects of Angelica dahurica on obesity and fatty liver in mice

Angelica dahurica (A. dahurica) is a traditional Chinese medicinal plant being used in clinical practice. The present study demonstrated that A. dahurica could reduce white-fat weight in high-fat-diet hyperlipidemic mice, decrease total cholesterol and triglyceride concentrations in the livers of both high-fat-diet and Triton WR1339 induced hyperlipidemic mice, and enhance the total hepatic lipase activities of them. These findings were further supported by the results derived from the experiments with HepG2 cells in vitro. In addition, the proteins related to lipids metabolism were investigated using LC-MS/MS, indicating that genes of lipid metabolism and lipid transport were regulated by A. dhurica. The results from LC-MS/MS were further conformed by Western blot and real time PCR assays. A. dahurica could down-regulate the expression of catalase (CAT) and sterol carrier protein2 (SCP2) and up-regulate the expression of lipid metabolism related genes-lipase member C (LIPC) and peroxisome proliferator-activated receptor gamma (PPARγ). In the Triton WR1339 mouse liver and HepG2 cells in vitro, A. dahurica was able to increase the expression of LIPC and PPARγ, confirming the results from in vivo experiments. Imperatorin showed the same activity as A. dahurica, suggesting it was one of the major active ingredients of the herb. In conclusion, our work represented a first investigation demonstrating that A. dahurica was able to regulate lipid metabolism and could be developed as a novel approach to fighting against fatty liver and obesity.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Mitochondrial H2O2 signaling is controlled by the concerted action of peroxiredoxin III and sulfiredoxin: Linking mitochondrial function to circadian rhythm

Mitochondria produce hydrogen peroxide (H₂O₂) during energy metabolism in most mammalian cells as well as during the oxidation of cholesterol associated with the synthesis of steroid hormones in steroidogenic cells. Some of the H₂O₂ produced in mitochondria is released into the cytosol, where it serves as a key regulator of various signaling pathways. Given that mitochondria are equipped with several H₂O₂-eliminating enzymes, however, it had not been clear how mitochondrial H₂O₂ can escape destruction by these enzymes for such release. Peroxiredoxin III (PrxIII) is the most abundant and efficient H₂O₂-eliminating enzyme in mitochondria of most cell types. We found that PrxIII undergoes reversible inactivation through hyperoxidation of its catalytic cysteine residue to cysteine sulfinic acid, and that release of mitochondrial H₂O₂ likely occurs as a result of such PrxIII inactivation. The hyperoxidized form of PrxIII (PrxIII-SO₂H) is reduced and reactivated by sulfiredoxin (Srx). We also found that the amounts of PrxIII-SO₂H and Srx undergo antiphasic circadian oscillation in mitochondria of the adrenal gland, heart, and brown adipose tissue of mice maintained under normal conditions. Cytosolic Srx was found to be imported into mitochondria via a mechanism that requires formation of a disulfide-linked complex with heat shock protein 90, which is likely promoted by H₂O₂ released from mitochondria. The imported Srx was found to be degraded by Lon protease in a manner dependent on PrxIII hyperoxidation state. The coordinated import and degradation of Srx underlie Srx oscillation and consequent PrxIII-SO₂H oscillation in mitochondria. The rhythmic change in the amount of PrxIII-SO₂H suggests that mitochondrial release of H₂O₂ is also likely a circadian event that conveys temporal information on steroidogenesis in the adrenal gland and on energy metabolism in heart and brown adipose tissue to cytosolic signaling pathways.

Effect of Ankaferd Blood Stopper on Skin Superoxide Dismutase and Catalase Activities in Warfarin-Treated Rats

AIM

Ankaferd Blood Stopper (ABS) is a new promising local hemostatic agent, and its mechanism on hemostasis has been shown by many studies. However, the effects of ABS on skin superoxide dismutase (SOD) and catalase (CAT) activities have not been investigated before. The aim of this study was to evaluate the effects of this new generation local hemostatic agent on warfarin-treated rats focusing on its the antioxidant potential in short-term soft tissue healing.

METHODS

Twelve systemically warfarin treated (warfarin group) and 12 none treated Wistar Albino rats (control group) were selected for the trial. Rats in the warfarin group were treated intraperitonally with 0.1 mg/kg warfarin, and rats in the control group were given 1 mL/kg saline 3 days earlier to surgical procedure and continued until killing. All rats had incisions on dorsal dermal tissue, which was applied ABS or no hemostatic agent before suturing. Six of each group were killed on day 4, and the other 6 were killed on day 8. Blood and skin samples were taken. Prothrombin time (PT) in blood samples, CAT, and SOD activities in skin samples were determined.

RESULTS

Warfarin treatment dose was found to be convenient and warfarin treatment increased the PT levels as expected. Warfarin treatment decreased CAT activity significantly compared to the control group. The ABS treatment significantly increased SOD activities in the warfarin group at the end of the eighth day.

CONCLUSION

Ankaferd Blood Stopper acted positively in short-term tissue healing by increasing SOD activity in warfarin-treated rats. Therefore, ABS may be suggeted as a promoting factor in tissue healing.

Mitochondrial ROS Metabolism: 10 Years Later

The role of mitochondria in oxidative stress is well recognized, but many questions are still to be answered. This article is intended to update our comprehensive review in 2005 by highlighting the progress in understanding of mitochondrial reactive oxygen species (ROS) metabolism over the past 10 years. We review the recently identified or re-appraised sources of ROS generation in mitochondria, such as p66(shc) protein, succinate dehydrogenase, and recently discovered properties of the mitochondrial antioxidant system. We also reflect upon some controversies, disputes, and misconceptions that confound the field.

Mitochondrial physiology and reactive oxygen species production are altered by hypoxia acclimation in killifish (Fundulus heteroclitus)

Many fish encounter hypoxia in their native environment, but the role of mitochondrial physiology in hypoxia acclimation and hypoxia tolerance is poorly understood. We investigated the effects of hypoxia acclimation on mitochondrial respiration, O2kinetics, emission of reactive oxygen species (ROS), and antioxidant capacity in the estuarine killifish ( ITALIC! Fundulus heteroclitus). Killifish were acclimated to normoxia, constant hypoxia (5 kPa O2) or intermittent diel cycles of nocturnal hypoxia (12 h:12 h normoxia:hypoxia) for 28-33 days and mitochondria were isolated from liver. Neither pattern of hypoxia acclimation affected the respiratory capacities for oxidative phosphorylation or electron transport, leak respiration, coupling control or phosphorylation efficiency. Hypoxia acclimation also had no effect on mitochondrial O2kinetics, but ITALIC! P50(the O2tension at which hypoxia inhibits respiration by 50%) was lower in the leak state than during maximal respiration, and killifish mitochondria endured anoxia-reoxygenation without any impact on mitochondrial respiration. However, both patterns of hypoxia acclimation reduced the rate of ROS emission from mitochondria when compared at a common O2tension. Hypoxia acclimation also increased the levels of protein carbonyls and the activities of superoxide dismutase and catalase in liver tissue (the latter only occurred in constant hypoxia). Our results suggest that hypoxia acclimation is associated with changes in mitochondrial physiology that decrease ROS production and may help improve hypoxia tolerance.

To involvement the conformation of the adenine nucleotide translocase in opening the Tl(+)-induced permeability transition pore in Ca(2+)-loaded rat liver mitochondria

The conformation of adenine nucleotide translocase (ANT) has a profound impact in opening the mitochondrial permeability transition pore (MPTP) in the inner membrane. Fixing the ANT in 'c' conformation by phenylarsine oxide (PAO), tert-butylhydroperoxide (tBHP), and carboxyatractyloside as well as the interaction of 4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS) with mitochondrial thiols markedly attenuated the ability of ADP to inhibit the MPTP opening. We earlier found (Korotkov and Saris, 2011) that calcium load of rat liver mitochondria in medium containing TlNO3 and KNO3 stimulated the Tl(+)-induced MPTP opening in the inner mitochondrial membrane. The MPTP opening as well as followed increase in swelling, a drop in membrane potential (ΔΨmito), and a decrease in state 3, state 4, and 2,4-dinitrophenol-uncoupled respiration were visibly enhanced in the presence of PAO, tBHP, DIDS, and carboxyatractyloside. However, these effects were markedly inhibited by ADP and membrane-penetrant hydrophobic thiol reagent, N-ethylmaleimide (NEM) which fix the ANT in 'm' conformation. Cyclosporine A additionally potentiated these effects of ADP and NEM. Our data suggest that conformational changes of the ANT may be directly involved in the opening of the Tl(+)-induced MPTP in the inner membrane of Ca(2+)-loaded rat liver mitochondria. Using the Tl(+)-induced MPTP model is discussed in terms finding new transition pore inhibitors and inducers among different chemical and natural compounds.

Protective effect of Crocin against zearalenone-induced oxidative stress in liver and kidney of Balb/c mice

Zearalenone (ZEN) is a mycotoxin from Fusarium species commonly found in many food commodities and known to cause reproductive disorders. Several studies have shown that ZEN is hematotoxic and hepatotoxic and causes several alterations of immunological parameters. In the present study, we aimed to evaluate the protective effect of Crocin (CRO), a natural carotenoid, against ZEN-induced toxicity in both renal and hepatic tissues of Balb/c mice. We demonstrated that ZEN (40 mg/kg body weight (b.w.)) induced oxidative stress in both kidney and liver as monitored by measuring the malondialdehyde (MDA) level, the protein carbonyl generation, the catalase and superoxide dismutase activity, and the expression of the heat shock proteins (Hsp70). However, combined treatment of ZEN with different doses of CRO (50, 100, and 250 mg/kg b.w.) significantly reduced ZEN-induced alterations in all tested oxidative stress markers. It could be concluded that CRO was effective in the protection against ZEN-induced toxicity in the liver and kidney of Balb/c mice.

Interactions between mitochondrial reactive oxygen species and cellular glucose metabolism

Mitochondrial reactive oxygen species (ROS) production and detoxification are tightly balanced. Shifting this balance enables ROS to activate intracellular signaling and/or induce cellular damage and cell death. Increased mitochondrial ROS production is observed in a number of pathological conditions characterized by mitochondrial dysfunction. One important hallmark of these diseases is enhanced glycolytic activity and low or impaired oxidative phosphorylation. This suggests that ROS is involved in glycolysis (dys)regulation and vice versa. Here we focus on the bidirectional link between ROS and the regulation of glucose metabolism. To this end, we provide a basic introduction into mitochondrial energy metabolism, ROS generation and redox homeostasis. Next, we discuss the interactions between cellular glucose metabolism and ROS. ROS-stimulated cellular glucose uptake can stimulate both ROS production and scavenging. When glucose-stimulated ROS production, leading to further glucose uptake, is not adequately counterbalanced by (glucose-stimulated) ROS scavenging systems, a toxic cycle is triggered, ultimately leading to cell death. Here we inventoried the various cellular regulatory mechanisms and negative feedback loops that prevent this cycle from occurring. It is concluded that more insight in these processes is required to understand why they are (un)able to prevent excessive ROS production during various pathological conditions in humans.

Vitex agnus-castus L. (Verbenaceae) Improves the Liver Lipid Metabolism and Redox State of Ovariectomized Rats

Vitex agnus-castus (VAC) is a plant that has recently been used to treat the symptoms of menopause, by its actions on the central nervous system. However, little is known about its actions on disturbances in lipid metabolism and nonalcoholic fat liver disease (NAFLD), frequently associated with menopause. Ovariectomized (OVX) rats exhibit increased adiposity and NAFLD 13 weeks after ovary removal and were used as animal models of estrogen deficiency. The rats were treated with crude extract (CE) and a butanolic fraction of VAC (ButF) and displayed the beneficial effects of a reduction in the adiposity index and a complete reversion of NAFLD. NAFLD reversion was accompanied by a general improvement in the liver redox status. The activities of some antioxidant enzymes were restored and the mitochondrial hydrogen peroxide production was significantly reduced in animals treated with CE and the ButF. It can be concluded that the CE and ButF from Vitex agnus-castus were effective in preventing NAFLD and oxidative stress, which are frequent causes of abnormal liver functions in the postmenopausal period.

A novel enzyme with spermine oxidase properties in bovine liver mitochondria: identification and kinetic characterization

The uptake of spermine into mammalian mitochondria indicated the need to identify its catabolic pathway in these organelles. Bovine liver mitochondria were therefore purified and their capacity for natural polyamine uptake was verified. A kinetic approach was then used to determine the presence of an MDL 72527-sensitive enzyme with spermine oxidase activity in the matrix of bovine liver mitochondria. Western blot analysis of mitochondrial fractions and immunogold electron microscopy observations of purified mitochondria unequivocally confirmed the presence of a protein recognized by anti-spermine oxidase antibodies in the mitochondrial matrix. Preliminary kinetic characterization showed that spermine is the preferred substrate of this enzyme; lower activity was detected with spermidine and acetylated polyamines. Catalytic efficiency comparable to that of spermine was also found for 1-aminododecane. The considerable effect of ionic strength on the Vmax/KM ratio suggested the presence of more than one negatively charged zone inside the active site cavity of this mitochondrial enzyme, which is probably involved in the docking of positively charged substrates. These findings indicate that the bovine liver mitochondrial matrix contains an enzyme belonging to the spermine oxidase class. Because H2O2 is generated by spermine oxidase activity, the possible involvement of the latter as an important signaling transducer under both physiological and pathological conditions should be considered.

Pathophysiological implications of mitochondrial oxidative stress mediated by mitochondriotropic agents and polyamines: the role of tyrosine phosphorylation

Mitochondria, once merely considered as the "powerhouse" of cells, as they generate more than 90 % of cellular ATP, are now known to play a central role in many metabolic processes, including oxidative stress and apoptosis. More than 40 known human diseases are the result of excessive production of reactive oxygen species (ROS), bioenergetic collapse and dysregulated apoptosis. Mitochondria are the main source of ROS in cells, due to the activity of the respiratory chain. In normal physiological conditions, ROS generation is limited by the anti-oxidant enzymatic systems in mitochondria. However, disregulation of the activity of these enzymes or interaction of respiratory complexes with mitochondriotropic agents may lead to a rise in ROS concentrations, resulting in oxidative stress, mitochondrial permeability transition (MPT) induction and triggering of the apoptotic pathway. ROS concentration is also increased by the activity of amine oxidases located inside and outside mitochondria, with oxidation of biogenic amines and polyamines. However, it should also be recalled that, depending on its concentration, the polyamine spermine can also protect against stress caused by ROS scavenging. In higher organisms, cell signaling pathways are the main regulators in energy production, since they act at the level of mitochondrial oxidative phosphorylation and participate in the induction of the MPT. Thus, respiratory complexes, ATP synthase and transition pore components are the targets of tyrosine kinases and phosphatases. Increased ROS may also regulate the tyrosine phosphorylation of target proteins by activating Src kinases or phosphatases, preventing or inducing a number of pathological states.

Molecular strategies for targeting antioxidants to mitochondria: therapeutic implications

Mitochondrial function and specifically its implication in cellular redox/oxidative balance is fundamental in controlling the life and death of cells, and has been implicated in a wide range of human pathologies. In this context, mitochondrial therapeutics, particularly those involving mitochondria-targeted antioxidants, have attracted increasing interest as potentially effective therapies for several human diseases. For the past 10 years, great progress has been made in the development and functional testing of molecules that specifically target mitochondria, and there has been special focus on compounds with antioxidant properties. In this review, we will discuss several such strategies, including molecules conjugated with lipophilic cations (e.g., triphenylphosphonium) or rhodamine, conjugates of plant alkaloids, amino-acid- and peptide-based compounds, and liposomes. This area has several major challenges that need to be confronted. Apart from antioxidants and other redox active molecules, current research aims at developing compounds that are capable of modulating other mitochondria-controlled processes, such as apoptosis and autophagy. Multiple chemically different molecular strategies have been developed as delivery tools that offer broad opportunities for mitochondrial manipulation. Additional studies, and particularly in vivo approaches under physiologically relevant conditions, are necessary to confirm the clinical usefulness of these molecules.

Increased reactive oxygen species production during reductive stress: The roles of mitochondrial glutathione and thioredoxin reductases

Both extremes of redox balance are known to cause cardiac injury, with mounting evidence revealing that the injury induced by both oxidative and reductive stress is oxidative in nature. During reductive stress, when electron acceptors are expected to be mostly reduced, some redox proteins can donate electrons to O2 instead, which increases reactive oxygen species (ROS) production. However, the high level of reducing equivalents also concomitantly enhances ROS scavenging systems involving redox couples such as NADPH/NADP+ and GSH/GSSG. Here our objective was to explore how reductive stress paradoxically increases net mitochondrial ROS production despite the concomitant enhancement of ROS scavenging systems. Using recombinant enzymes and isolated permeabilized cardiac mitochondria, we show that two normally antioxidant matrix NADPH reductases, glutathione reductase and thioredoxin reductase, generate H2O2 by leaking electrons from their reduced flavoprotein to O2 when electron flow is impaired by inhibitors or because of limited availability of their natural electron acceptors, GSSG and oxidized thioredoxin. The spillover of H2O2 under these conditions depends on H2O2 reduction by peroxiredoxin activity, which may regulate redox signaling in response to endogenous or exogenous factors. These findings may explain how ROS production during reductive stress overwhelms ROS scavenging capability, generating the net mitochondrial ROS spillover causing oxidative injury. These enzymes could potentially be targeted to increase cancer cell death or modulate H2O2-induced redox signaling to protect the heart against ischemia/reperfusion damage.

Antioxidant Potential of Plumieride against CCl₄-Induced Peroxidative Damage in Rats

In search of a new potent as an antioxidant from natural sources, plumieride—an iridoid isolated from the methanol extract of the bark of Plumeria bicolor (family Apocynaceae) was evaluated for its antioxidant potential against CCl₄-induced peroxidative damage in liver of rats. The antioxidant potential was evaluated by using hepatic tissue for SOD (superoxide dismutase), CAT (catalase), GSH (reduced glutathione), GPx (glutathione peroxidase), GR (glutathione reductase) and LPO (lipid peroxidation) alongwith the concomitant blood serum for AST & ALT (aspartate and alanine transaminases), GGT (gamma glutamyl transpeptidase), ALP (alkaline phosphatase), total bilirubin and total protein contents. All the biochemical parameters were significantly (p ≤ 0.001) altered by CCl₄ (0.3 mL/kg body weight/twice a week, intra-peritoneally for 30 days). Simultaneously, oral treatment with plumieride (5, 10 and 20 mg/kg body weight/day for 30 days), restored all the parameters towards a normal level, remarkably. The histological findings of liver sections further corroborated the antioxidant potential of plumieride compared with standard drug-silymarin. In conclusion, plumieride consists of sugar molecules, which have alcoholic groups. Therefore, the alcoholic groups of sugar increase its antioxidant potential through intermolecular hydrogen bonding along with the thiol(SH) group of non-protein thiols and enzymes resulting in the restoration of the antioxidant system. Therefore, it might be considered a natural antioxidant against peroxidative damage in rats.

Evaluation of Antioxidant and Hepatoprotective Activities of Moringa oleifera Lam. Leaves in Carbon Tetrachloride-Intoxicated Rats

The antioxidant and hepatoprotective activities of the extract of Moringa oleifera leaves were investigated against CCl₄-induced hepatotoxicity in rats. Hepatotoxic rats were treated with ethanol extract of Moringa oleifera for a period of 60 days at the following three dose levels; 100, 200 and 400 mg/kg body weight/day, orally. The activities were studied by assaying the serum marker enzymes like SGOT, SGPT, GGT, LDH, ALP, ACP, as well as total bilirubin, total protein and albumin in serum concomitantly with the activities of LPO, SOD, CAT, GSH, GR and GPx in liver. The activities of all parameters registered a significant (p ≤ 0.001) alteration in CCl₄ treated rats, which were significantly recovered towards an almost normal level in rats co-administered with M. oleifera extract in a dose-dependent manner. All the biochemical investigations were confirmed by the histopathological observations and compared with the standard drug. silymarin. Results suggest that the antioxidant and hepatoprotective activities of M. oleifera leaves are possibly related to the free radical scavenging activity which might be due to the presence of total phenolics and flavonoids in the extract and/or the purified compounds β-sitosterol, quercetin and kaempferol, which were isolated from the ethanol extract of M. oleifera leaves.

Are oxidative stress mechanisms the common denominator in the progression from hepatic steatosis towards non-alcoholic steatohepatitis (NASH)?

Non-alcoholic fatty liver disease (NAFLD) is not a single disease entity, rather it describes a spectrum of liver conditions that range from fatty liver (steatosis) to more severe steatosis coupled with marked inflammation and fibrosis [non-alcoholic steatohepatitis (NASH)] to severe liver disease such as cirrhosis and possibly hepatocellular carcinoma. Obesity, notably abdominal obesity, is a common risk factor for NAFLD. The pathogenesis from steatosis to NASH is poorly understood, and the 'two hit' model, as suggested nearly two decades ago, provides a feasible starting point for characterization of underlying mechanisms. This review will examine the oxidative stress factors ('triggers') which have been implicated as a 'second hit' in the development of primary NASH. It would be reasonable to assume that multiple, rather than single, pro-oxidative intracellular and extracellular triggers act in conjunction promoting oxidative stress that drives the development of NASH. It is likely that the common denominator of these pro-oxidative triggers is mitochondrial dysfunction. Understanding the contribution of each of these 'triggers' is an essential step in starting to understand and elucidate the mechanisms responsible for progression from steatosis to NASH, thus enabling the development of therapeutic targeting to prevent NASH development and progression.

Protective effect of Actiniopteris radiata (Sw.) Link. against CCl₄ induced oxidative stress in albino rats

ETHNOPHARMACOLOGICAL RELEVANCE

Actiniopteris radiata is a herb with great medicinal value and is evaluated for hepatoprotective activity. To investigate the protective effect of ethanolic extract of Actiniopteris radiata (EEAR) on CCl₄ induced oxidative stress in male Wistar albino rats.

MATERIALS AND METHODS

EEAR were administered for 8 consecutive weeks to rats. Group I - control; Group II - toxin control (30% CCl₄); Group III and Group IV received EEAR (250 and 500 mg/kg respectively). Antioxidant status in liver were estimated by determining the activities of the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx); as well as by determining the levels of lipid peroxidation (LPO) and reduced glutathione (GSH). In addition, isoenzyme pattern and mRNA expression of the antioxidants were studied. Partial characterization of EEAR was performed by Liquid chromatography-mass spectrometry (LC-MS).

RESULTS

CCl₄ induced oxidative stress as evidenced from increase in LPO along with reduction of SOD, CAT, GPx and GSH. Treatment with EEAR (250 and 500 mg/kg) mitigated the CCl₄ induced oxidative stress. An analysis of the isozyme pattern of these antioxidant enzymes revealed variations in SOD2, CAT, GPx2 and GPx3 in CCl₄ treated rats, which were normalized after EEAR treatment. Furthermore, expression of genes for the antioxidant enzymes, were down-regulated by CCl₄ treatment, which were reversed by EEAR. The results of partial characterization of EEAR by LC-MS revealed the presence of rutin and other 7 unknown phenolic derivatives.

CONCLUSIONS

These findings suggest the protective effect of EEAR against CCl₄ induced oxidative stress might be attributed to the presence of flavonoids and phenolic compounds.

Nicotinamide nucleotide transhydrogenase (Nnt) links the substrate requirement in brain mitochondria for hydrogen peroxide removal to the thioredoxin/peroxiredoxin (Trx/Prx) system

Mitochondrial reactive oxygen species are implicated in the etiology of multiple neurodegenerative diseases, including Parkinson disease. Mitochondria are known to be net producers of ROS, but recently we have shown that brain mitochondria can consume mitochondrial hydrogen peroxide (H2O2) in a respiration-dependent manner predominantly by the thioredoxin/peroxiredoxin system. Here, we sought to determine the mechanism linking mitochondrial respiration with H2O2 catabolism in brain mitochondria and dopaminergic cells. We hypothesized that nicotinamide nucleotide transhydrogenase (Nnt), which utilizes the proton gradient to generate NADPH from NADH and NADP(+), provides the link between mitochondrial respiration and H2O2 detoxification through the thioredoxin/peroxiredoxin system. Pharmacological inhibition of Nnt in isolated brain mitochondria significantly decreased their ability to consume H2O2 in the presence, but not absence, of respiration substrates. Nnt inhibition in liver mitochondria, which do not require substrates to detoxify H2O2, had no effect. Pharmacological inhibition or lentiviral knockdown of Nnt in N27 dopaminergic cells (a) decreased H2O2 catabolism, (b) decreased NADPH and increased NADP(+) levels, and (c) decreased basal, spare, and maximal mitochondrial oxygen consumption rates. Nnt-deficient cells possessed higher levels of oxidized mitochondrial Prx, which rendered them more susceptible to steady-state increases in H2O2 and cell death following exposure to subtoxic levels of paraquat. These data implicate Nnt as the critical link between the metabolic and H2O2 antioxidant function in brain mitochondria and suggests Nnt as a potential therapeutic target to improve the redox balance in conditions of oxidative stress associated with neurodegenerative diseases.

Redox-modulated phenomena and radiation therapy: the central role of superoxide dismutases

SIGNIFICANCE

Ionizing radiation is a vital component in the oncologist's arsenal for the treatment of cancer. Approximately 50% of all cancer patients will receive some form of radiation therapy as part of their treatment regimen. DNA is considered the major cellular target of ionizing radiation and can be damaged directly by radiation or indirectly through reactive oxygen species (ROS) formed from the radiolysis of water, enzyme-mediated ROS production, and ROS resulting from altered aerobic metabolism.

RECENT ADVANCES

ROS are produced as a byproduct of oxygen metabolism, and superoxide dismutases (SODs) are the chief scavengers. ROS contribute to the radioresponsiveness of normal and tumor tissues, and SODs modulate the radioresponsiveness of tissues, thus affecting the efficacy of radiotherapy.

CRITICAL ISSUES

Despite its prevalent use, radiation therapy suffers from certain limitations that diminish its effectiveness, including tumor hypoxia and normal tissue damage. Oxygen is important for the stabilization of radiation-induced DNA damage, and tumor hypoxia dramatically decreases radiation efficacy. Therefore, auxiliary therapies are needed to increase the effectiveness of radiation therapy against tumor tissues while minimizing normal tissue injury.

FUTURE DIRECTIONS

Because of the importance of ROS in the response of normal and cancer tissues to ionizing radiation, methods that differentially modulate the ROS scavenging ability of cells may prove to be an important method to increase the radiation response in cancer tissues and simultaneously mitigate the damaging effects of ionizing radiation on normal tissues. Altering the expression or activity of SODs may prove valuable in maximizing the overall effectiveness of ionizing radiation.